Signaling method and network element for a virtual private network

ABSTRACT

The present invention relates to a signaling method and network element for a virtual private network, wherein a destination capability is determined in response to the receipt of a connection request from a subscriber belonging to the virtual private network. Based on the determination result, an initiation of a virtual private network signaling in the call set-up is decided. Thereby, the signaling load can be reduced already in the originating point if the destination is not able to support the signaling required for the virtual private network. The capability determination may be based on a private numbering plan required for a number translation in the telecommunication network.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a U.S. national stage application under 35 U.S.C. §371 ofinternational stage application No. PCT/EP99/09387, filed on Dec. 1,1999, which date is hereby the filing date of this application under 35U.S.C. §363.

FIELD OF THE INVENTION

The present invention relates to a signaling method and a networkelement for a telecommunication network providing a virtual privatenetwork (VPN).

BACKGROUND OF THE INVENTION

The VPN concept allows private traffic traditionally served by leasedprivate lines to share the existing trunk capacity of the PSTN (PublicSwitched Telecommunication Network). This allows for a more efficientutilization of network resources and provides a number of benefits toboth operators and users. Network costs can be more closely tied toactual usage. With private networks, the cost of inter-site traffic istied to the maximum capacity required, not overall usage. VPN alsoallows for increased flexibility in configuring the network.

QSIG (unified international corporate network signaling standard) is anISDN common channel signaling system designed for use in corporatenetworks. It was developed in an open forum for all major European PBXmanufacturers. The name QSIG refers to signaling across the ISDN “Q”reference point which is the logical signaling point between two PINXs.QSIG defines a set of protocols for the interaction of PINXs, so thatcommon sets of services and features, with similar appearances, areavailable to users across private networks, including multi-sitenetworks.

The original standards for QSIG were developed by the ECMA (EuropeanComputer Manufacturers Association). Later, these standards were used asa basis for the ETSI (European Telecommunications Standards Institute).The main standards covering the Basic Call Protocol are Layer 2 ETS 300402-1 based on ITU-T Q.920 and Layer 3 ETS 300 172 (for the PSS1signaling system) based on ISO/IEC 11572, or EN 301 060 (for the DSS1+signaling system).

In addition thereto, a standard which covers the Core Generic FunctionalProtocol for supplementary services for private telecommunicationnetworks has been developed by ISO (ISO/IEC 11582) and given the ETSIidentification ETS 300 239. This is the core protocol that theindividual supplementary services use to avail of the transport servicesof the underlying layers.

A VPN product provides QSIG interfaces for interconnecting remote PINXs(Private Integrated Services Network Exchanges) across the PSTN, eithervia a single exchange or via a number of exchanges in the network.Conceptionally, the entire exchange network is seen by the end PINXs asa simple transit network.

The transport of the QSIG signaling over the PSTN (e.g. ISDN network) isaccomplished by “enveloping” QSIG messages within ISUP (ISDN User Part)messages. This method enables common ISUP signaling links and associatedbearers to be provisioned for VPN and non-VPN traffic for greaterefficiency.

To be able to offer a true on-net call and to provide for thetransparent transfer of QSIG messages over the PSTN from the VPN entrypoint to the VPN exit point (when the VPN extends over multipleexchanges), a technique called Application Transport Mechanism (APM) isused. This means that a call is set up over the PSTN to provide for theconnection, and all associated QSIG data is transmitted along the callwith the APM mechanism. The receiving end extracts the data and sends anidentical message to the destination PINX. Thus, PINXs see the networkas a dedicated private network with QSIG signaling.

Since there may be parts of the PSTN that do not support the signaling,or the destination subscriber is not capable of supporting the protocol,a method is defined in the ETSI specification EN 301 062-1 to drop thecall to support only a basic call. When such a situation is detected, aso-called gateway function is performed and the necessary parts of theprivate network signaling are transformed to a PSTN signaling. Thismethod is specified in such a way that the QSIG information is alwayscarried with the call set up in the PSTN. If transparency is lost, i.e.the destination does not support QSIG, then the QSIG data is droppedfrom subsequent messages in a gateway function of the network after thiscondition is detected. Hence, the initial OSIG signalling leads to anincreased load in the signaling network.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide asignaling method and network element for a telecommunication networkproviding a virtual private network, by means of which the signalingload in the telecommunication network can be decreased.

This object is achieved by a signaling method for a telecommunicationnetwork providing a virtual private network, said signaling methodcomprising the steps of:

determining a destination capability in response to the receipt of aconnection request from a subscriber belonging to the virtual privatenetwork; and

deciding on the initiation of a virtual private network signaling in thecall set-up, based on the determination result in said determinationstep.

Furthermore, the above object is achieved by a network element forinitiating a signaling in a telecommunication network providing avirtual private network, the network element comprising:

determining means for determining a destination capability in responseto the receipt of a connection request from a subscriber belonging tothe virtual private network; and

signaling control means for deciding on the initiation of a virtualprivate network signaling in the call set-up, based on the determinationresult of said determining means.

Accordingly, a pre-defined signaling load decrease is enabled bychecking the destination capability during the initiation of a set-upprocedure in the originating point. If the destination is not able tosupport the signaling, the originating node performs a gateway functionwithout initiating the VPN signaling in the call set-up. Since it isknown that certain types of VPN members do not support the VPN signalingin the first place (e.g. mobile terminals, old PBXs (Private BranchExchanges)), the load produced by the set-up signaling for these memberscan be reduced. Known standardized methods may still be used as aback-up for those nodes that can change to support the VPN signaling inthe future (e.g. international VPN members).

Preferably, the destination capability may be determined on the basis ofa private numbering plan which may be stored at the originating node.Alternatively, the private numbering plan may be stored in an IN(Intelligent Network) node located at the originating node of theconnection request. In particular, the virtual private network signalingmay not be initiated if the private numbering plan indicates a mobilesubscriber as the destination of the call.

Preferably, the network element may be an originating node of theconnection request. Particularly, the network element may be a networkexchange.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greaterdetail on the basis of a preferred embodiment with reference to theaccompanying drawings, in which:

FIG. 1 shows a corporate network for providing a QSIG featuretransparency, to which the present invention can be applied;

FIG. 2 shows a basic diagram of a VPN group signaling according to thepreferred embodiment of the present invention;

FIG. 3 shows a basic flow diagram of a signaling method according to thepreferred embodiment of the present invention; and

FIG. 4 shows a basic block diagram of a network element for initiating asignaling, according to the preferred embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, the preferred embodiment of the method and networkelement according to the present invention will be described on thebasis of a corporate network structure as shown in FIG. 1.

According to the corporate network shown in FIG. 1, a first networkexchange DX1 and a second network exchange DX2 are connected via a PSTN,such as an ISDN network. The network exchanges DX1 and DX2 provide for adirectly terminated QSIG interface. The QSIG Access is a 2 Mbit/sinterface which implements up to thirty 64 kbit/s B-channels and one 64kbit/s virtually B-channel structure (30B+D structure). However, otheraccess structures such as a 2B+D structure are possible, as well. The“star” architecture shown in FIG. 1 allows QSIG ports to be provisionedmore efficiently. A single QSIG port can be utilized to carry traffic toany or all other points in the VPN. In addition to supporting privatetraffic, the QSIG interfaces can provide a gateway functionality tocarry traffic to and from the PSTN, resulting in increased efficiency inthe provision of access ports. The VPN is always customer-specific andthe system must be configured to suit the particular customer'srequirements. The provision of the VPN network may be based on asoftware product running on the network exchanges DX1 and DX2. Themaximum number of VPN groups depends on the data standard for theswitches involved. A VPN indicator in the signaling defines the contextto be used. In particular, a PINX connected to one of the networkexchanges DX1 and DX2 can be marked to be conforming to specificreference or service entry points.

In case that a call set-up contains a VPN indicator, a VPN call is setup as requiring QSIG feature transparency. Otherwise, a basic call isinitiated. A business group ID as defined by ETSI can be set against aVPN group, and the ID is sent with each call to the network to identifythat the call is a business group call. The business group ID can be setagainst the group in a global format.

According to FIG. 1, a first private branch exchange PBX1 and a secondprivate branch exchange PBX2 are connected to the network exchange DX2.In addition thereto, a Centrex group is connected to the second networkexchange DX2, wherein the term “Centrex” indicates the provision oftelecommunication services similar to a private branch exchange (PBX)from the second network exchange DX2. Thus, a Centrex group can replacea PBX or a key telephone system. Furthermore, a third private branchexchange PBX3 and a Mobile Switching Center (MSC) of a mobile networkare connected to the first network exchange DX1.

Additionally, the network exchanges DX1 and DX2 are arranged to providea Service Switching Point (SSP) function of an IN (Intelligent Network).To achieve this, the network exchanges DX1 and DX2 are connected to aService Control Point (SCP) of the IN. Thereby, the control of a privatenumbering plan (PNP) which allows for creation of an individualnumbering scheme for each customer VPN can be concentrated to a singlepoint in the network, wherein the IN is used to store the translationtable of the VPN. In this case, the network exchanges DX1 and DX2 in theVPN use only the site codes to route the call to an SSP. In the SSP, thetranslated number triggers the call to be routed to the SCP. The SCPthen translates the number to a DDI (Direct Dialing In) number defininga particular extension in a PINX.

Alternatively, in case the IN is not used for the number translation,the PNP may be stored in the network exchanges DX1 and DX2.

As can be gathered from the diagram shown in FIG. 1, the second andthird private branch exchanges PBX2 and PBX3 support the QSIG signaling.The same applies to Centrex group. In contrast thereto, the firstprivate branch exchange PBX1 is arranged to use another signalingsystem, i.e. DSS 1 (Digital Subscriber Signaling System No. 1), and istherefore part of the VPN without the features available for QSIG nodes.The site code feature enables also mobile users to be included in thesame numbering plan as the QSIG VPN users. Accordingly, a QSIG featuretransparency is achieved for the users inside the dotted line of FIG. 1.

According to the preferred embodiment, the network exchanges DX1 and DX2are arranged to decide in dependence on the destination capabilitywhether a QSIG signaling is initiated in the set-up of a call, or not,in case a call from a private branch exchange or a Centrex groupbelonging to the VPN is to be established. Thereby, the signaling loadin the VPN group can be reduced for those VPN members not supporting theQSIG signaling. When a user dials a number of a mobile member of the VPNgroup, no QSIG signaling is carried with the call. In case of a call toanother member of the VPN group, which supports the QSIG signaling, theQSIG signaling is initiated. Thereby, the signaling load is reducedalready in the originating point, wherein an information about thecapability of the VPN group members may be derived e.g. from the PNP oranother suitable table or data base provided either in the originatingnode (e.g. network exchange DX1 or DX2) or in a separate node locatedclose to the originating node (e.g. an IN node).

In case the destination does not support the QSIG signaling, therespective network exchange DX1 or DX2 performs a gateway function anddrops unnecessary information relating to the QSIG signaling from theset-up messages. Nevertheless, some VPN features such as the PNP orspecial charging functions may as well be supported towards the VPNgroup members not supporting the QSIG signaling. Thus, in the case shownin FIG. 1, the QSIG signaling is not initiated towards the first privatebranch exchange PBX1 and the Mobile Switching Center MSC.

FIG. 2 shows a principal diagram of a capability determination performedin the first network exchange DX1 based on the PNP of the establishedVPN. In this case, the first network exchange DX1 provides for thenumber translation function between private numbers and public networkaddresses, to subsequently enable the routing of calls across the PSTN.Each customer VPN or corporate VPN is allowed to have different PNPnumber translation rules, and the network exchange DX1 determines thetranslation based on the corporate VPN to which the originated callbelongs.

The private number length can be fixed or variable for each VPN, from 3to 8 digits. This flexibility allows users with existing privatenetworks to be cut-over to the VPN service without modifications to theexisting numbering plan. The originating network exchange performs thePNP number translation from the private number to the public form for acall set-up over the public network. Routing within the public networkthen always uses translated numbers.

According to FIG. 2, the first network exchange DX1 initiates the QSIGsignaling on the basis of the first digit(s) of the number indicated inthe PNP. In case the number starts with the digit “2”, a call isestablished to one of the Centrex extension numbers defined between 211and 299. Therefore, the QSIG signaling is initiated. The same applies tothe case where the number in the PNP starts with the digit “3”, whichindicates one of the PBX extension number of the PBX2, ranging between3111 and 3999. Moreover, in case the number in the PNP starts with thedigits “9”, or “0”, the call is to be established to an attendantconnected to the VPN network as a separate node, or to an external PSTNnumber, respectively, for which the support of the QSIG signaling cannotbe decided unambiguously. Therefore, the QSIG signaling is alsoinitiated, such that the conventional standardized method can be used asa back-up feature.

However, if the number starts with “82”, the call is to be establishedto one of the mobile extension numbers ranging between 82611 and 82699.In this case, the QSIG signaling is not initiated, since it is knownthat mobile terminals do not support the QSIG signaling. The sameapplies to the specific numbers defined for the first private branchexchange PBX1 according to FIG. 1.

The capability determination may be based on a number comparisonoperation, or a flag or a bit may be provided which is set in a table(e.g. PNP table) used in the number analysis, so as to indicate therequirement of QSIG signaling initiation.

As already mentioned, the number translation in the network exchangesDX1 and DX2 may as well be based on a translation table (e.g. PNP)stored in an IN node.

FIG. 3 shows a basic flow diagram of the signaling method performed inthe network exchanges DX1 and DX2.

When a set-up request is received from a connected end terminal in stepS100, the network exchange determines based e.g. on the VPN indicator,whether a VPN call is to be established (step S101). If not, the flowproceeds to step S106, where a set-up procedure of a basic call isperformed.

If a VPN call is determined in step S101, the destination capability forthe VPN signaling (e.g. QSIG signaling) is checked in step S102. Thismay be based e.g. on the PNP translation table stored in the networkexchange or in the IN.

Then, in step S103, it is checked whether the destination supports theVPN signaling (e.g. QSIG signaling), or not (step S103). If not, the VPNsignaling information included in the received set-up messages isdropped (step S105) and the procedure proceeds to step S106, where theset-up procedure of the basic call is performed. Thus, the networkexchange only performs a gateway function.

If the result of the determination in step S103 indicates that thedestination supports the VPN signaling, the flow proceeds to step S104,where the set-up procedure for a VPN call, including the VPN signaling(e.g. QSIG signaling), is performed.

FIG. 4 shows a basic block diagram of those parts of the networkexchanges DX1 and DX2 which are essential for performing the presentinvention. According to FIG. 4, a switching unit 10 is provided forperforming the required switching function between the private branchexchanges PBX1 to PBX3, the PSTN, the Centrex group and the mobilenetwork, i.e. the members of the VPN group. In case a set-up request isreceived via the switching unit 10, it is supplied to a capabilitydetermination unit 12 arranged to determine the capability of the calldestination based on a number translation table stored in a PNP database 11. It is noted that the PNP database 11 is not required if thedestination capability is determined by referring to an IN numbertranslation function. The determination result obtained in thecapability determination unit 12 is supplied to a signaling control unit13 arranged to generate the signaling required for setting up the call.Thus, according to the preferred embodiment, the signaling control unit13 generates a signaling for setting up a basic call, and drops areceived VPN signaling information, in case the determination resultreceived from the capability determination unit 12 indicates that thedestination does not support the VPN signaling. Otherwise, the signalingcontrol unit 13 initiates the VPN signaling and performs the set-upprocedure of the VPN call.

The functional blocks 11 to 13 indicated in FIG. 4 may be realized asconcrete hardware structures or as routines of a control program adaptedto control a processing means (e.g. CPU) provided in the respectivenetwork element.

It is to be noted that the present invention may be applied to anytelecommunication network providing a virtual private network functionwhich requires support of a predetermined VPN signaling at a respectivedestination node. Furthermore, the signaling method according to thepreferred embodiment may be performed in any network element arrangedfor initiating a set-up signaling in a telecommunication network. Theabove description of the preferred embodiment and the accompanyingdrawings are therefore only intended to illustrate the presentinvention. The preferred embodiment of the invention may very within thescope of the attached claims.

In summary, the present invention relates to a signaling method andnetwork element for a virtual private network, wherein a destinationcapability is determined in response to the receipt of a connectionrequest from a subscriber belonging to the virtual private network.Based on the determination result, an initiation of a virtual privatenetwork signaling in the call set-up is decided. Thereby, the signalingload can be reduced already in the originating point, if the destinationis not able to support the signaling required for the virtual privatenetwork. The capability determination may be based on a privatenumbering plan used for a number translation in the telecommunicationnetwork.

Thus, while there have been shown and described and pointed outfundamental novel features of the present invention as applied to apreferred embodiment thereof, it will be understood that variousomissions and substitutions and changes in the form and details of thedevices described and illustrated, and in their operation, and of themethods described may be made by those skilled in the art withoutdeparting from the spirit of the present invention. For example, it isexpressly intended that all combinations of those elements and/or methodsteps which perform substantially the same function in substantially thesame way to achieve the same results are within the scope of theinvention. Substitutions of elements from one described embodiment toanother are also fully intended and contemplated. It is the intention,therefore, to be limited only as indicated by the scope of the claimsappended hereto.

What is claimed is:
 1. A signaling method for a telecommunicationnetwork providing a virtual private network, said signaling methodcomprising the steps of: a) determining a destination capability tosupport virtual private network signaling in response to the receipt ofa connection request from a subscriber belonging to said virtual privatenetwork, wherein said destination capability is determined on the basisof a table used in a number analysis; b) deciding on the initiation of avirtual private network signaling in the call set-up, when thedetermination result in said determination step indicates that thedestination is able to support virtual private network signaling, and c)dropping an information relating to said virtual private networksignaling, if it is determined in said determination step that thedestination is not able to support said virtual private networksignaling; wherein said virtual private network signaling is notinitiated if said table indicates a mobile subscriber as the destinationof the call.
 2. The method according to claim 1, wherein said virtualprivate network signaling is a QSIG signaling.
 3. The method accordingto claim 1, wherein said table is a private numbering plan stored in anIN node located at the originating node of said connection request. 4.The method according to claim 1, wherein said signaling method isperformed in an originating node of said connection request.
 5. Anetwork element for initiating a signaling in a telecommunicationnetwork providing a virtual private network, said network elementcomprising: determining means for determining a destination capabilityto support virtual private network signaling in response to the receiptof a connection request from a subscriber belonging to said virtualprivate network, wherein said determining means is arranged to determinesaid destination capability by referring to a table used in a numberanalysis; and signaling control means for deciding on the initiation ofa virtual private network signaling in the call set-up, when thedetermination result in said determination step indicates that thedestination is able to support virtual private network signaling,wherein the network element is adapted to drop an information relatingto said virtual private network signaling, if it is determined in saiddetermining means that the destination is not able to support saidvirtual private network signaling; and wherein said virtual privatenetwork signaling is not initiated if said table indicates a mobilesubscriber as the destination of the call.
 6. The network elementaccording to claim 5, wherein said determining means is arranged toobtain a private numbering plan (PNP) from an IN node located at saidnetwork element.
 7. The network element according to claim 5, whereinsaid signaling control means is arranged to drop an information relatingto said virtual private network signaling from a set-up message and toperform a gateway function for said set-up message.
 8. The networkelement according to claim 5, wherein said network element is anoriginating node of said connection request.
 9. The network elementaccording to claim 8, wherein said network element is a networkexchange.
 10. A method for reducing signaling in a telecommunicationnetwork which supports at least one virtual private network (VPN),wherein there are at least two signalling protocol systems forsignalling within said at least one VPN, said signaling reduction methodcomprising the steps of: receiving a connection request from anorigination subscriber in a VPN, wherein said requested connection isbetween said origination VPN subscriber and a destination VPNsubscriber; determining a capability of the destination VPN subscriberto support a first VPN signalling protocol system, wherein said firstVPN signalling protocol system is a system for the interaction ofprivate integrated service exchanges (PINXs) in the VPN, wherein saidstep of determining the capability to support the first VPN signalingprotocol system comprises the sub-step of: accessing a private numberingplan (PNP) function, wherein said PNP function provides for translatingbetween private VPN addresses and public network addresses, and whereinsaid PNP function also provides for said step of determining thedestination VPN subscriber capability to support the first VPN signalingprotocol system; and initiating set up of the requested VPN connectionusing the first VPN signaling protocol system if it is determined thatthe destination VPN subscriber supports the first VPN signaling protocolsystem, or initiating set up of the VPN connection without using thefirst VPN signaling protocol if it is determined that the destinationVPN subscriber does not support the first VPN signaling protocol system.11. The method of claim 10, wherein the first VPN signaling protocolsystem comprises a QSIG signalling system.
 12. The method of claim 11,wherein at least one VPN subscriber does not have the capability tosupport QSIG signalling because said at least one VPN subscriber iseither a mobile terminal or on a private branch exchange (PBX) incapableof QSIG signalling.
 13. The method of claim 10, wherein the PNP functioncomprises a PNP translation table.
 14. The method of claim 10, whereinsaid PNP function provides for said step of determining the capabilityto support the first VPN signaling protocol system of the destinationVPN subscriber either by providing an indicia in a PNP translation tableor based on a numerical comparison of specific digits within the VPNprivate address of the destination VPN subscriber.
 15. The method ofclaim 14, wherein the indicia in the PNP translation table is at leastone of a flag and a bit.
 16. The method of claim 10, wherein thetelecommunication network supports a plurality of VPNs, and each of theplural VPNs have a different PNP function.
 17. The method of claim 10,wherein the PNP function is provided either in an originating networknode or in a separate network node near to the originating network node.18. The method of claim 17, wherein the originating network node or theseparate network node comprises at least one of a network exchange, anintelligent network (IN) node, and a switching unit.
 19. The method ofclaim 10, further comprising the step of: initiating set up of therequested VPN connection using first VPN signaling protocol system if itcannot be unambigiously determined whether the destination VPNsubscriber supports first VPN signaling protocol system.